Packaged light emitting diodes (packaged LEDs) are being used as light sources in an increasing variety of applications extending from communications and instrumentation to household and automotive lighting and image display. Packaged LEDs are now being considered for nearly all functions being performed by incandescent light bulbs.
One factor limiting the full potential of packaged LEDs is the thermal limits of conventional packaging. The commercially prevalent packaging assembly disposes semiconductor LED die in a plastic package. In these assemblies, both the die and the plastic package are temperature sensitive. The temperature sensitivity (reduced light generation) of the die has been ameliorated by refining the purity of the semiconductor materials. Improved LED die will now operate at about 120° C. But plastic LED packages typically have an operational limit of about 80° C. Meanwhile, the industry now seeks packaged LED assemblies that can operate at 200° C. Thus, the potential applications of LEDs are now limited by the thermal limits of packaging.
Another limiting factor is the relatively high cost of fabricating and mounting packaged LED assemblies. There exist highly promising fabrication techniques such as surface mount technology (SMT) and bolt down assembly (BDA), but these approaches typically require solder reflow temperatures that are too high for use with conventional plastic packaging and mounting. Thus, lower cost production of LED packages is also constrained by the thermal limits of conventional packaging. Accordingly, there is a need for an improved light emitting diode assembly packaged for surface mounting and higher temperature operation.